Golf ball manufacturers are constantly trying to achieve the perfect balance between feel and performance. The physical characteristics of a golf ball are determined by the combined properties of the core, any intermediate layers, and the cover, which are, in turn, determined by the chemical compositions of each layer. For example, a particular composition used for a cover layer may increase distance while another composition may provide improved spin.
For example, golf ball covers formed from balata allow players to achieve spin rates sufficient to control ball direction and distance, particularly on shorter shots. However, balata covers are easily damaged. In contrast, golf balls covers formed from ionomer resins provide higher durability and overall distance, but lack the spin and feel of balata-covered balls. And, unlike ionomer-covered golf balls, polyurethane covered golf balls can be formulated to possess the soft “feel” of balata covered golf balls, however, golf ball covers made from polyurethane have not, to date, fully matched ionomer-covered golf balls with respect to resilience or the rebound of the golf ball cover. In addition, polyurethane-covered golf balls may be susceptible to yellowing (due to the use of aromatic components) and moisture absorption. Paints and moisture barrier layers may be used to counteract against the yellowing and moisture absorption in polyurethane-covered balls.
Polyurea materials have recently come onto the scene for golf ball layer materials due to the improved resilience and adherence to layers formed of different materials. In addition, because polyurea-based compositions may be formed from aliphatic materials, the yellowing of aromatic polyurethane-covered golf balls is typically not an issue for aliphatic polyurea-covered golf balls. Similar to polyurethane, however, because a polyurea golf ball cover is generally softer than a thermoplastic ionomer golf ball cover, the coefficient of restitution does not compare to an ionomer-covered golf ball.
In addition, conventional polyurea compositions have several characteristics that are undesirable for golf equipment applications including uncontrollable reaction rates, non-homogenous mixtures, poor adhesion, shrinkage, and non-optimal chemical resistance. For example, the reaction times for conventional polyurea compositions are very fast, i.e., an aliphatic isocyanate and an aliphatic amine may react and gel in about 5 seconds, which make it difficult to control the formation of the composition. In addition, several reactions may take place in a polyurea composition, which result in a non-homogenous mixture. For instance, a first reaction may take place between the highly reactive components followed by subsequent reactions between the less reactive components. The non-homogenous nature may affect the finish, properties, and consistency of the resultant composition. Furthermore, fast reactions between the amine and isocyanate generally do not allow adequate time for the polyurea to penetrate and adhere to a substrate.
Silicone materials have also been used in golf balls to purportedly increase the coefficient of restitution and/or durability based on their innate ability to provide materials having fairly high ultimate elongation. The use of such materials, however, has been primarily limited to interior layers of a golf ball. For example, U.S. Pat. No. 6,159,110 discloses the use of silicone polymers, silicone fluids, silicone elastomers, and silicone resins in interior golf ball layers. In addition, like conventional polyurea materials, conventional silicone materials have several characteristics that are undesirable, including low-moderate tensile strengths. Furthermore, the use of silicone elastomers in the manufacture of golf balls requires covalent crosslinking because linear or branched silicone (polydimethylsiloxane) (PSX) homopolymers are viscous liquids or millable gums at room temperature.
Regardless of how the cross vulcanization is effected, the resulting thermoset silicone cannot be re-dissolved or re-melted, which severely reduces the number of options for post-fabrication operations. For example, thermal forming, radio frequency welding, heat sealing and solvent bonding are essentially unavailable when working with conventional silicone elastomers. Once formed, however, the infinite network provides the polymer its rubber elasticity and characteristic physical-mechanical properties.
In light of the independent benefits and deficiencies discussed above for the various materials, it would be advantageous to incorporate the favorable properties of each individual material into a composition for use in golf balls so that the strengths of each material can be maximized and the weaknesses minimized. For example, there is a need in the art for a polyurea-based or polyurethane-based composition with a controllable reaction rate, homogenous properties, and increased durability and impact resistance. The present invention seeks to address these needs through the use of polymer alloying and blending.